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Patented Apr. 22,

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INDUCTION MOTOR.

Application fled Kay 28,

To all whom. it may concern:

subject of the King of Sweden, residing at Nahant, in the county of Essex, State'of Massachusetts, have invented certain new and useful Improvements in Induction Motors, of which the following is a specification.

My invention relates to induction motors and particularly to the secondary members It is well known that one of the ditliculties met with in the operation of induction motors having seconda-r members provided with squirrel ca e windings is the loss of torque or dea points at startin and at sub-synchronous speeds. This difficulty 'has been overcome heretofore by the choice of the best possible ratio. between the number of slots'in primary and, secondary members. This has not always solved the difficulty, however, as'it has been found that frequently with the best ratio of slots there has occurred a loss of torque at sub-synchronous s eed's in certain induction motors. In accor ance with my invention, I have solved this difliculty in a new, and novel wal he slots in the secondary mem er of the motor.

. Other features of novelty which characterize my invention will be pointed out with articularly in the claims annexed to and orming a part of this specification. For a better understanding of my invention, however, reference may be had to the following description taken in accordance with the accompanying drawing in which Fig. 1 is an' end view of the secondary member of an induction motor embodying my invention, with parts broken away, and Fig. 2 is a crosssectional view of the secondary member of Fig. 1 taken on the line 2-2. v

n the drawing, there is shown the secondary member of an induction motor, which I have illustrated as a rotor. It comprises laminations A mounted -in the usual manner on a shaft B. The laminations are provided with slots arranged in grou s, the slots in one lgq'roup being numbered. m 1 to 8 and in t e next adjacent group 9 to 15, the slots of each group being unequally spaced apart. The slots are provided with conductors connected together b usual end rings C to form a short circuite or squirrel. cage winding. It will be noted from the which consists in an une ualditions in the motor.

192:. Serial no. 641,887.

drawing that the spacings between adjacent Q slots in the group numbered 1 to 8. gradnally increase, so that the spacing between slots 1 and 2 is a minimum and the spacing between slots 7 and 8 is a maximum, and the spacing between adjacent-slots inthe adjacent group, numbered 9 to"15, gradually decrease a am to aminimum, so that the spacing etween slots 14 and 15 is substantially the same as the spacing between slots 1 and 2.. U

In order to obtain the best operating characteristics with a winding disposed in slots in accordance with my invention, I make the cross-sectional area of the slots and the conductors in the slots, which arespaced far apart, greater than the cross-sect onal area of the slots and the conductors in the slots which are spaced close together. The crosssectional area of the conductors gradually increases. from a minimum in slot 1 to a maximum in slot 8, and then radually decreases again to a minimum in s 0t 15. The reason for this change in cross-section is to cause the current to distribute .evenly over the whole secondary windin .that is, equally around the periphery of t e secondary member when the machineis operating under full load conditions. In the drawing, I have shown the grou of conductors from 1 130 15 equal to a po e itch, and in the motor shown there are our such groups. This is an advantageous arrangement and will insure balanced connecessar and the groups of unequally spaced s ots ma be less or even greater than to secondary members whenused as stators of induction motors.

I desire it to be understood that I aim in the appended claims to cover all such' modifications and any others which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. In an induction motor, a secondary member comprising laminations provided with slots, said slots being arranged in grou s, the slots of, each group being unq y Spaced apart, and conductors in said u It is, however, not

cage winding.

2. In an induction motor, a secondary member comprising laminations provided with slots, said slots being arranged in groups, the slots of each group being unequally spaced apart, the spacing between adjacent slots in one group gradually increasing to a maximum and the spacing between adjacent slots in the adjacent group decreasing to a minimum, and conductors in said slots connected together to form a squirrel cage winding.

3. In an induction motor, a secondary member comprising laminations provided with slots, said slots being arranged in groups, the slots of each group being unequally spaced apart, and conductors in said slots connected together to form a squirrel cage winding, the cross-sectional area of the conductors in the slots spaced far apart being greater than the cross-sectional area of the conductors in the slots spaced close together.

member comprising laminations provided with slots, said slots being arranged in groups, the slots of each group being unequally spaced apart, the spacing between adjacent slots in one group gradually increasing to a maximum and the spacing between adjacent slots in the adjacent group, decreasing to a minimum, and conductors in said slots connected together to form a squirrel age winding, the cross-sectional area of the conductors in the slots in one group gradually increasing to a maximum and vthe cross-sectional area of the conductois in the slots of the adjacent group decreasing to a minimum, the cross-sectional area of the COIldllCtOl'S in the slots spaced far apart being greater than the cross-sectional area of the conductors in the slots spaced close together.

In witness whereof, I have hereunto set my hand this th day of May, 1923.

SVEN R. BERGMAN. 

